No start - Crank sensor issue?

#1

Finally got everything back together in time for Mid Ohio.

Turn key.

No start.

I followed this: http://www.spece30.com/forum/41-electrical-gauges-and-sensors/53136-no-start-no-spark-totally-stumped (JLevie’s post) and the only thing I found wrong was…

“2) Check the resistance across DME 47 & 48, which should be 500-560 ohms. If the CPS is dismounted, the resistance can be seen to change
from about 500 to 540-540 when a ferrous object is brought to the face of the sensor. Neither pin should be grounded.”

I pulled the connector off of the crank sensor and am seeing 0.547 kOhm across terminals 1 and 2 so I think the sensor itself is alright but I’m not seeing the same resistance across pins 47 and 48. It’s 12:30 and time for bed so I can’t trace the wires tonight but does anyone know offhand how the sensor makes its way to the ECM?

Also, do you think it has anything to do with this: http://spece30.com/forum/41-electrical-gauges-and-sensors/66337-thats-not-gone-well

#2

I just checked continuity from the ECM to the connector for the crank position sensor and found that there’s continuity between the second pin on the sensor connector and pin 48 on the DME but no continuity from the first pin on the sensor connection and pin 47 on the DME but there’s continuity when checking the DME ground pins so there’s definitely an issue with the engine harness wiring somewhere.

I’m thinking that it might have to do with me drilling into the wiring harness. Does anyone know if there’s a way to remove the DME connector so that I can trace which wires go to what pins on the DME?

#3

Starter doesn’t run or engine doesn’t catch? My guess is the latter.

Pull the fuel line, stick it in a jar, and fire the starter. If you get fuel than CPS ok. If you don’t get fuel then jumper fuel relay (forward pin to left pin) and confirm the fuel will pump.

If jummping relay gets you fuel but starting doesn’t, then it’s back to looking at CPS.

Start there then we will move on.

This is the kind of problem where having a fuel pressure gauge on your dash is very nice.

#4

[quote=“Ranger” post=66927]Starter doesn’t run or engine doesn’t catch? My guess is the latter.

Pull the fuel line, stick it in a jar, and fire the starter. If you get fuel than CPS ok. If you don’t get fuel then jumper fuel relay (forward pin to left pin) and confirm the fuel will pump.

If jummping relay gets you fuel but starting doesn’t, then it’s back to looking at CPS.

Start there then we will move on.

This is the kind of problem where having a fuel pressure gauge on your dash is very nice.[/quote]

The engine cranks but never catches.

I can check the fuel pump at lunch but I pulled one of the plugs last night and wasn’t getting spark.

I know for a fact that I don’t have continuity to the pin 1 of the crank sensor to DME pin 47 though so I think that’s the problem especially since I haven’t really touched anything else related since the car last ran.

Is there any way to remove the Bosch ECM connector “cover” without just cutting it apart?

#5

Do the tests suggested above. It’s important to find a way to confirm test results. Otherwise it’s painfully easy to get mislead by a bad test result and spend painful hours chasing a shadow.

#6

Bridged the fuel pump relay and fuel is flowing. No fuel during cranking. By the way you want to bridge 30 and 87 on the FPR which correspond to the left and front, respectively.

I have power to the coil with key on but no spark when cranking.

#7

Ok, that’s good confirmation.

Quit testing for spark as your indicator of a good CPS, that’s just going to get you zapped. Instead test for fuel flow when the starter is running. Think of the test for spark as a way of confirming that your FPR is good.

You’re certain that CPS cable and plug wire sensor cable are not switched?

At the CPS wire-to-harness connector, lets test the pins on the CPS wire and see what we get. That should tell us if it’s an engine harness issue or a CPS/CPS wire issue. Jim’s test where you pass a piece of steel near the magnet sounds like a great test.

#8

I couldn’t find anything to fit between the sensor and the toothed wheel so I just hooked up the voltmeter and then cranked the engine.

The resistance drops from 541 ohms to right around 500 ohms and then back to 541 ohms as the tooth goes past the sensor.

I’m heading back to work now so I’ll pick things back up around 6pm or so.

#9

[quote=“MrDomino” post=66922]I just checked continuity from the ECM to the connector for the crank position sensor and found that there’s continuity between the second pin on the sensor connector and pin 48 on the DME but no continuity from the first pin on the sensor connection and pin 47 on the DME but there’s continuity when checking the DME ground pins so there’s definitely an issue with the engine harness wiring somewhere.

I’m thinking that it might have to do with me drilling into the wiring harness. Does anyone know if there’s a way to remove the DME connector so that I can trace which wires go to what pins on the DME?[/quote]
It sounds to me like you have found the problem. The harness contains two small coax wires from the CPS connector to the DME connector. You can pull the covers at end and check to see if there is a failed connection. Otherwise the failure is within the harness.

I have three harnesses that have suffered internal failures. Two had CPS problems and the third had a problem with the gauge and ECT sensors. I opened up one of the harnesses that had a CPS problem with the idea of running new coax. But a close examination of all of the wires in the harness suggested that would be a poor, short term, solution. There was noticeable damage to other wires, so another failure was imminent. So I bought a brand new engine and fuel/sensor harness from BMW. It had to come from Germany and wasn’t cheap. But it should be good for another 20 years.

#10

Is there any easy way to open up the ECM connector? I think the issue is a result of my accidental drilling of the wiring harness but it happened pretty close to the connector so there’s not enough room to fix it. If I could open up the connector I should have enough room to cut it and resolder as a solution until the end of the year.

#11

A new harness isn’t a crazy idea. In the several times I had to do surgery on a harness I was each time taken aback by how bad the condition of the conductors were. The wiring was tarnished dark black well back inside of their sheathing plastic. It’s a wonder that any of the wires still have a decent electrical connection with the crimped on connector.

Re. tracing which wire goes to which DME pin. You should be able to do this with wire color alone. I think that with few exceptions like ground and 12V, every wire color going to the DME is unique.

#12

According to JLevie it’s some sort of coaxial cable. I’m thinking about cutting part of the connector off to give me about an inch more wire. Hopefully I can fix that part of the wire.

If there was an easy way of getting the DME connector cover off so I could see all of the pins this would be an extremely simple fix. The only problem is that if I cut it off there’s not going to be any way of keeping the wiring harness connected to the DME.

#13

So I ended up breaking off part of the plastic DME connector on the wire harness side (not the DME connector side) to give me enough room to cut the damaged section of the wire out and splice in a connector. The wire is shielded and there’s two wires inside the shield so it was kind of a pain in the ass but after soldering in some extra wire I saw 0.547 kOhm across DME pins 47 and 48 and the engine started right up.

#14

Even the oil pressure and battery voltage gauges I wired in worked without issue!

MID OHIO IN TWO DAYS!

#15

That was fine work. Now get yourself a spare harness or two.

#16

Yeah, I will.

JLevie, where did you get your harness from?

#17

[quote=“MrDomino” post=66953]Yeah, I will.

JLevie, where did you get your harness from?[/quote]
I bought it from my dealer.